Dispersion of linear and non-linear optical susceptibilities for amino acid 2-aminopropanoic CH 3 CH(NH 2 )COOH single crystals: experimental and theoretical investigations Ali Hussain Reshak, * ab S. Auluck, c Dalibor Stys, a I. V. Kityk, d H. Kamarudin, b J. Berdowski e and Z. Tylczynski f Received 26th May 2011, Accepted 19th August 2011 DOI: 10.1039/c1jm12361k A comprehensive experimental and theoretical investigation of dispersion of the linear and nonlinear optical susceptibilities for amino acid L-alanine single crystals is reported. The state-of-the-art full potential linear augmented plane wave method, within a framework of the density functional theory was applied. The atomic positions from X-ray diffraction have been optimized so that the force on each atom is around 1 mRy au 1 . This relaxed geometry has been used for the theoretical calculations. The complex dielectric susceptibility dispersion, its zero-frequency limit and the birefringence of amino acid L-alanine single crystals were studied. The crystal exhibits a large uniaxial dielectric anisotropy resulting in a significant birefringence. The calculated birefringence at static limit is 0.072 and 0.074 at l ¼ 1064 nm (corresponding to 1.165 eV) in good agreement with the measured value (0.073). We also report calculations of the complex second-order optical susceptibility dispersions for the principal tensor components: c (2) 123 (u), c (2) 231 (u) and c (2) 312 (u). The calculated second order susceptibility tensor components |c (2) 123 (u)|, |c (2) 231 (u)|, and |c (2) 312 (u)| at l ¼ 1064 nm are compared with those obtained from our measurements performed using the 25 ps Nd:YAG pulsed laser at l ¼ 1064 nm. Our calculations are in reasonably good agreement with our experimental data. In addition we have calculated the microscopic second order hyperpolarizability, b 123 , vector component along the principal dipole moment directions for the dominant component c (2) 123 (u) and it is found to be 0.21  10 21 pm V 1 in the static limit and 0.27  10 21 pm V 1 at 1.165 eV (l ¼ 1064 nm) in comparison with our measured value (0.31  10 21 pm V 1 ) at l ¼ 1064 nm. Additional study of the second order susceptibilities versus the external laser treatment is performed. I. Introduction Organic non-linear optical crystals are of particular interest for design and formation of different laser operated optoelectronic materials such as modulators, deflectors, optical triggers, opti- cally operated fibers, etc. This is due to their large second-order optical susceptibilities, ultra-fast response time (sub-picosecond) and high optical damage thresholds. One of the restraining factors in organic materials engineering for such kinds of mate- rials is the absence of reliable relation between the origin of the chemical bonds, optical resonance and the output susceptibili- ties. Most of the research is devoted to the study of integrated nonlinear optical constants without a serious analysis of the principal resonances contributing to the output second order susceptibilities which determine the efficiency of optical second harmonic generation (SHG). In our previous works 1,2 we have demonstrated the effectiveness of such approach both for the inorganic KTiOPO 4 as well as organic 3-methyl-4-phenyl-5-(2- pyridyl)-1,2,4-triazole for nonlinear applications. The principal novelty of our approach is a detailed analysis of the dispersion of the nonlinear optical susceptibilities and for particular reso- nances of the corresponding optical functions. The latter are defined by the concrete chemical bonding. So there exists a rela- tionship between the origin of optical susceptibilities and the corresponding chemical bonds. Additionally important infor- mation can be obtained from comparison of the microscopic hyperpolarizabilities and the macroscopic second order suscep- tibilities. The dispersion of the susceptibilities can be used to a Institute of Physical Biology, South Bohemia University, Nove Hrady, 37333, Czech Republic. E-mail: maalidph@yahoo.co.uk; Fax: +420-386 361231; Tel: +420 777729583 b School of Material Engineering, Malaysia University of Perlis, P.O. Box 77, d/a Pejabat Pos Besar, 01007 Kangar, Perlis, Malaysia c National Physical Laboratory Dr K S Krishnan Marg, New Delhi, 110012, India d Electrical Engineering Department, Technological University of Czestochowa, Al.Armii Krajowej 17/19, Czestochowa, Poland e Institute of Physics, J. Dlugosz University of Czestochowa, Armii Krajowej Av.13/15, 42-200 Czestochowa, Poland f Faculty of Physics, A. Mickiewicz University, Umultowska Av. 85, 61-614 Poznan, Poland This journal is ª The Royal Society of Chemistry 2011 J. Mater. Chem., 2011, 21, 17219–17228 | 17219 Dynamic Article Links C < Journal of Materials Chemistry Cite this: J. Mater. Chem., 2011, 21, 17219 www.rsc.org/materials PAPER